In general, a reciprocating motor is formed by modifying an induction magnetic field of a motor with a cubic structure to a flat shape, so that a flat shaped mover is mounted at an upper side of a stator formed flat and moved linearly according to a magnetic field change.
Recently, a reciprocating motor has been introduced that a stator is separated into an outer stator and an inner stator formed in a cylindrical shape which are arranged overlapped with a certain gap therebetween, a mover assembly is movably disposed between the outer stator and the inner stator, a winding coil is mounted at either one of the outer stator and the inner stator, and permanent magnets are attached at the corresponding mover assembly, so that the mover can be reciprocally moved in an axial direction of the reciprocating motor by an induction magnetic field generated by the winding coil.
As shown in FIG. 1, a conventional reciprocating motor includes: a stator 10 forming an induction magnetic field, and a mover assembly 20 reciprocally moved according to the induction magnetic field of the stator 10.
The stator 10 includes an outer stator 11 formed in a hollow cylindrical shape as a plurality of laminations are stacked and having a winding coil (C) therein, and an inner stator 12 formed in a hollow cylindrical shape as a plurality of iron pieces are stacked and inserted into the outer stator 11 with a certain gap therebetween.
The mover assembly 20 includes a mover body 21 formed in a cylindrical shape and disposed movably between the outer stator 11 and the inner stator 12, permanent magnets 22 mounted at equal intervals at an outer circumference surface of the mover body 21 corresponding to the winding coil (C) of the stator 10, and a magnet cover 23 formed in a cylindrical shape to cover the permanent magnets 22, and forcibly press-fit, bent or welded to the outer circumferential surface of the permanent magnets 22.
Reference numeral 21a is a permanent magnet mounting groove.
The operation of the conventional reciprocating motor for a compressor will now be described.
When a current is applied to the winding coil (C), an induction magnetic field is formed in different directions between the outer stator 11 and the inner stator 12 according to the direction of the current. The mover body 21 is reciprocally moved together with the permanent magnets 22 as they are drawn or pushed according to the direction of the induction magnetic field.
If a piston (not shown) is coupled at the mover body 21, the piston is reciprocally moved in a cylinder (not shown) together with the mover assembly 20, thereby compressing a fluid.
However, in the conventional reciprocating motor, as shown in FIG. 2, the permanent magnet cover 23 is formed in a cylindrical shape, but in case of the permanent magnets (M), there occurs a height difference (h) due to a processing error of each permanent magnet (M). Thus, causing a difficulty in the press-fit operation, and the permanent magnets 22 may be broken if they are forcibly press-fit or released from the mover body.
In order to solve the problem, the permanent magnet cover 23 may be press-fit and then fixed by a spot welding. In this respect, however, since the permanent magnet cover 23 is made of a thin plate material, there is a difficulty in the welding operation, and even if the welding is performed, its strength is weak, resulting in that the permanent magnet cover may be released.
In addition, for welding, the mover body 21 is limited to the metallic material, and if the metallic material is used, a magnetic force is leaked to degrade an efficiency of the motor.